A light-emitting diode (LED) is a semiconductor diode that emits light when an electrical current is applied in the forward direction of the device, such as in a simple LED circuit.
The device is fabricated from layers of silicon and seeded with atoms of phosphorus, germanium, arsenic or other rare-earth elements. The layers of the device are called the die and the junction between the materials is where the light is generated. The electricity enters from one side of the die and exits out the other. As the current passes through the LED device, the materials that makes up the junction react and light is emitted.
LEDs are widely used as indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting. A LED is usually a small area (less than 1 mm2) light source, often with optics added to the chip to shape its radiation pattern and assist in reflection. The color of the emitted light depends on the composition and condition of the semiconducting material used, and can be infrared, visible, or ultraviolet.
Combining red, green, and blue light-emitting diodes in the appropriate way allows lighting engineers to match the soft white light of incandescent bulbs. Also, combining red, green, and blue light-emitting diodes can be used to create other color light outputs or dynamic color light outputs for scores boards, advertisement boards and the like.
Because low cost white light emitting diodes are now available, blending or mixing of color LEDs for commercial or residential lighting application has largely been replaced with white light emitting diodes. White light emitting diodes are often characterized by a color temperature scale. The color temperature of any light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source. White light emitting LED's generally do not emit purely white light, but rather they emit a component of pure white light and varying amounts overtone colors. An LED color temperature defines the amount of pure white, yellow, red and blue emitted by the white light emitting diode. Another way to think of an LED color temperature is how ‘warm’ or ‘cool’ the light is that is emitted by white light emitting diode. A warmer white light emitting diode emits white light with overtone component of yellow or even red, while a cooler white light emitting diode emits white light with overtone components of blue.